Hard Disk Drives (HDDs) including an acceleration sensor have been widely known. When the HDD is dropped, the HDD itself detects the drop from an output from the acceleration sensor. Upon detecting the drop, heads are retracted from above magnetic disks. Therefore, damaging the heads and the magnetic disks on impact may be prevented.
Related documents are U.S. Pat. No. 7,031,094, Japanese Laid-open Patent Publication No. 2007-115309, Japanese Laid-open Patent Publication No. 06-103712, and Japanese Patent No. 3,821,642.
When the HDD is subjected to the drop impact, the magnetic disks may become misaligned in a radial direction or a spindle motor may be shifted. The misalignment of the disks or the spindle leads to a deterioration of an HDD's performance. For example, a correction value of the servo signal has a margin of error. As a result, data writing or reading takes much time.